Re: [PATCH] block, bfq: fix uaf for bfqq in bic_set_bfqq()

[Jan Kara <jack@suse.cz>]

On Fri 13-01-23 17:44:10, Yu Kuai wrote:
> After commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'"),
> bic->bfqq will be accessed in bic_set_bfqq(), however, in some context
> bic->bfqq will be freed first, and bic_set_bfqq() is called with the freed
> bic->bfqq.
> 
> Fix the problem by always freeing bfqq after bic_set_bfqq().
> 
> Fixes: 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
> Reported-and-tested-by: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Looks good, thanks for the fix! Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  block/bfq-cgroup.c  | 2 +-
>  block/bfq-iosched.c | 4 +++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> index a6e8da5f5cfd..feb13ac25557 100644
> --- a/block/bfq-cgroup.c
> +++ b/block/bfq-cgroup.c
> @@ -749,8 +749,8 @@ static void bfq_sync_bfqq_move(struct bfq_data *bfqd,
>  		 * old cgroup.
>  		 */
>  		bfq_put_cooperator(sync_bfqq);
> -		bfq_release_process_ref(bfqd, sync_bfqq);
>  		bic_set_bfqq(bic, NULL, true, act_idx);
> +		bfq_release_process_ref(bfqd, sync_bfqq);
>  	}
>  }
>  
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 815b884d6c5a..2ddf831221c4 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -5581,9 +5581,11 @@ static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
>  
>  	bfqq = bic_to_bfqq(bic, false, bfq_actuator_index(bfqd, bio));
>  	if (bfqq) {
> -		bfq_release_process_ref(bfqd, bfqq);
> +		struct bfq_queue *old_bfqq = bfqq;
> +
>  		bfqq = bfq_get_queue(bfqd, bio, false, bic, true);
>  		bic_set_bfqq(bic, bfqq, false, bfq_actuator_index(bfqd, bio));
> +		bfq_release_process_ref(bfqd, old_bfqq);
>  	}
>  
>  	bfqq = bic_to_bfqq(bic, true, bfq_actuator_index(bfqd, bio));
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR